The Effects of Process Parameters on Cutting Characteristics in Laser Cutting of 20 mm-Thick FRP (I) - Through-Cut Characteristics and Kerf Geometry -

A 20 mm-thick hand-lay-up GFRP plate, representative of small fishing-boat hulls, was cut in air with a high-power fiber laser to establish a through-cut process window for hull opening during capsized-vessel rescue. The laminate consisted of 26 plies of chopped-strand mat and woven roving in an unsaturated polyester matrix. With the nozzle diameter and stand-off fixed at 3 mm and 5 mm, respectively, laser power (4-8 kW), cutting speed (420-720 mm/min), nitrogen pressure (3-7 bar) and defocus (+5 to -10 mm) were varied. At 5 bar and zero defocus, no through-cut was obtained at 4 kW, whereas through-cuts were obtained at 420-480 mm/min at 6 kW and at 420-600 mm/min at 8 kW. The maximum through-cut speed of 660 mm/min was achieved at 8 kW either with -10 mm defocus at 5 bar or with zero defocus at 7 bar. Front kerf width and soot deposition depended on whether the rear kerf remained open rather than on line energy alone. Higher nitrogen pressure reduced soot and shifted the maximum heat-affected width toward the rear-face. Horizontal traces on the cutting surface were attributed to resin pyrolysis at ply interfaces, and a defocus of -5 mm caused combustion and should be avoided.